Femto cells—in-building-based wireless access points interfaced with a wired broadband network—are deployed generally to improve or augment indoor macro wireless coverage provided by a wireless network operator. Femto cells typically operate in licensed portions of the electromagnetic spectrum, and generally offer plug-and-play installation; e.g., automatic configuration of femto access point upon provisioning or first power-up. Improved or augmented indoor coverage includes stronger signal and improved reception (e.g., voice or data), ease of session or call initiation, and session or call retention as well. Coverage improvements via femto cells also can also mitigate customer attrition, by providing enhanced subscriber perceived and actual quality of service.
Coverage of a femto cell, or femto AP, is intended to be confined within the bounds of an indoor compound (e.g., a building with multiple floors), in order to mitigate interference among terminals covered by a macro cell and terminals covered by the femto AP. In addition, confined coverage can reduce cross-talk among terminals serviced by disparate, neighboring femto cells as well. To provide coverage, femto cells are typically deployed in frequency carrier(s) that are different from frequency carrier(s) employed in macro cells; for example, femto and macro network within Universal Mobile Telecommunication System (UMTS) deployment operate in such frequency carrier configuration. Thus, to exploit femto coverage, inter-frequency carrier scan(s) of wireless environment are necessary to ensure successful macro-to-femto handoff for devices.
By design and/or protocol, e.g., when operating in a technology framework such as UMTS, mobile devices commonly continue to operate with same radio technology and frequency carrier as long as radio link conditions permit. Battery life conservation and complexity associated with inter-frequency carrier reselection are included among reasons to mitigate switching to a disparate technology or frequency carrier; it takes more power for a mobile device to scan multiple frequency carriers instead of the frequency carrier that currently serves the mobile. Accordingly, inter-frequency carrier, or inter-carrier, scan(s) and reselection are typically conditional rather than routine, occurring only when serving radio link quality is below predetermined thresholds. In summary, intra-carrier reselection is based upon time and best server, but inter-carrier scanning and reselection depend upon loss of received quality relative to a defined threshold.
In deployment scenarios in which femto coverage is provided via different frequency carriers than macro coverage, the conditional nature of inter-frequency carrier scan can cause the mobile device to neglect frequency carrier(s) in which femto coverage is provided in instances (e.g., locations and times) where macro coverage received quality is satisfactory or ideal. Thus, continuation of intra-frequency carrier scanning under adequate macro coverage conditions can prevent the mobile device from reselecting femto coverage even when femto in-building-based service is expected or desired regardless of macro coverage.